Spacers

[naughty]

40 profile is the correct match for 17's.

that depends on the width of the wheel

the profile is actually the percentage in millimeters of the tyres width

so a 40 profile for a polo will only keep the rolling diameter constant is the width of the tyre is 205. but nevertheless a 45 profile while seeming safer is definitely going to change the rolling diameter of the complete wheel unless its on a very narrow tyre

the trick to this profile business is to remember that what it means is that the sidewall is going to be the profile percentage of the tyre width so its got a relation and it isnt a constant measurement - it varies according to tyre width

[gareth_oau]

this site allows you to play with tyre widths and profiles to keep the same rolling diameter

http://www.miata.net/garage/tirecalc.html

[GuyGTi]

this site allows you to play with tyre widths and profiles to keep the same rolling diameter

http://www.miata.net/garage/tirecalc.html

Great! So if i get a 205 40 17 (bit of stretch) Then it should be almost exactly the same apparently
Thanks for that site very handy.
Guy